#define setcontext(u) _setmcontext(&(u)->mc)
#define getcontext(u) _getmcontext(&(u)->mc)
typedef struct mcontext mcontext_t;
typedef struct ucontext ucontext_t;
struct mcontext {
	ulong pc; /* lr */
	ulong cr; /* mfcr */
	ulong ctr; /* mfcr */
	ulong xer; /* mfcr */
	ulong sp; /* callee saved: r1 */
	ulong toc; /* callee saved: r2 */
	ulong r3; /* first arg to function, return register: r3 */
	ulong gpr[19]; /* callee saved: r13-r31 */
	/*
	// XXX: currently do not save vector registers or floating-point state
	//	ulong	pad;
	//	uvlong	fpr[18];	/ * callee saved: f14-f31 * /
	//	ulong	vr[4*12];	/ * callee saved: v20-v31, 256-bits each * /
	*/
};

struct ucontext {
	struct {
		void* ss_sp;
		uint ss_size;
	} uc_stack;
	sigset_t uc_sigmask;
	mcontext_t mc;
};

void makecontext(ucontext_t*, void (*)(void), int, ...);
int swapcontext(ucontext_t*, const ucontext_t*);
int _getmcontext(mcontext_t*);
void _setmcontext(const mcontext_t*);
